The invention relates to a mixture and a method for imprinting textiles.
Currently used methods for imprinting textiles include the inkjet printing and the screen printing methods.
The inkjet printing process is widely used as a result of the rapid development of computer technology and, in the private sector, is primarily used for producing colored pictures on paper. This new technology has also moved into the industrial sector for textile imprinting and is currently used advantageously for designing patterns and producing small yardages. The inkjet printing systems presently available in the market place deliver printing resolutions ranging from 180 dpi to 720 dpi and work with 4 to 16 basic colors from the assortment of reactive, acid, dispersion, or pigment coloring agents. Above all, the pigment printing is of extreme and central importance because it can be used universally on different substrates. Depending on the print resolution, a printing speed of up to 150 m2/h is possible at the present time, which is sufficient for the pattern design and production of small batch sizes because of the extremely short set-up times.
Even though the inkjet printing permits an extremely flexible production of high-quality colored textiles, conventional fixation methods represent a limiting factor that keeps this technology from gaining ground. Standard fixation units, for example steamer units and dry fixation units, cannot be adapted to this innovative printing technique because of their size, thus negating at least in part the advantages achieved with the inkjet printing. The fact that fixation occurs offline, in a separate operational step, is a particular disadvantage. The fixation units of known systems using inkjet printers for the imprinting of textiles take the form of steamers, which are positioned downstream, immediately following the inkjet printers, and which more or less permit a thermal online fixation of the printing patterns with the aid of hot air or saturated steam. These types of systems have the disadvantage that in order to finish the print patterns on the textiles, the textiles must be rewashed in a last operational step to remove pretreatment chemicals and non-fixated coloring agent components. This post-treatment is carried out in a manner known per se with the aid of washing units and dryers. So far, the production of inkjet printing patterns has not yet been realized with an online method, which represents a limiting factor for the flexible production of individual printing patterns using the inkjet method. It is therefore the object to provide a fixation unit with small dimensions and extremely flexible use, which can be realized using strong UV light sources. However, this requires the development and the use of suitable UV hardenable printing inks.
The inks used for the inkjet printing method must meet a plurality of specific requirements, wherein the viscosity and surface tension among other things play a crucial role in the formulation of the printing ink. Inks which can be used in inkjet printers have a water-like ink viscosity of less than 6 mPas and a surface tension of 20 to 50 mN/m. To prevent the ink from drying inside the nozzles, hygroscopic additives such as ethylene glycol, urea, or glycerin must furthermore be added to the ink. In addition, the electrolyte content (salts) of the ink must be kept to the lowest possible level to prevent possible corrosion on the printing head. To avoid nozzle obstructions (nozzle diameter <20 μm), particle sizes of <1 μm are required. These boundary conditions for the printing inks are determined by the type of printing head used and are extremely narrowly defined. In the case of pigment coloring agents, the standard concentration for use in most cases is only around 2% since the ink viscosity can increase strongly because of the presence of the binding agent. If the binding agent share and the pigment share increase strongly, the ink viscosity in part also increases strongly, thus making it even harder or impossible to print with this ink. For that reason, mostly pure pigment inks without added binding agents are primarily used at the present time. The binding agent is applied during a separate step, in which the imprinted material is submerged for impregnation and the imprinted textile material is then thermally fixated in another separate operating step.
Several UV curable systems for the inkjet and screen printing methods have already been introduced in the market place, which for the most part are present as 100% systems and must be adapted to the required viscosity level by adding low-viscous, mostly toxic reactive diluting agents. The expression 100% system is understood to refer to systems, which harden and cure completely during the fixation process, meaning at 100%, after they are applied to the textiles. In the market place, systems of this type are not acceptable for textile applications because of the skin-sensitizing effect and the toxic potential of the monomers in the form of residual monomers with incomplete reaction in the hardened printing pattern. Added to this is the fact that the use of such 100% systems results in an unacceptable stiffening of the imprinted textile patterns and is therefore also not acceptable in the market place.
The option of lowering the viscosity to improve the printability by adding organic solvents with correspondingly low viscosity must be ruled out from the start for ecological reasons and is not acceptable for the inkjet printing on textiles, particularly textile material used for clothing. The use of water-dilutable systems is in principle conceivable for the textile finishing process. However, the water-dilutable UV hardenable printing inks for inkjet applications, described so far in the relevant literature, contain biologically non-degradable alkylphenol ethoxylates (APEO) as dispersing agents for the pigments, which will be banned in the near future because of their toxicity to fish and their toxic decomposition products. Also used in such formulations are dispersing agents on the basis of condensates from formaldehyde and aryl sulfonic acids, as well as naphthalene sulfonic acid formaldehyde condensates, which also decompose slowly biologically and furthermore have the problem that the skin-sensitizing formaldehyde forms again. Examples of these systems are described in the following German Patent Applications: 197 39 620 A1, 197 53 831 A1, 197 27 766 A1 and 197 27 767 A1. Owing to the above-described disadvantages, neither the 100% systems nor the water-dilutable UV hardenable systems have found their way into practical operations involving textile materials.
It is the object of the present invention to make possible an environment-friendly, highly efficient imprinting of textiles while ensuring a high quality and functionality of these textiles.